Oscillation generator



Dec. 26, 1933. v. J. ANDREW 1,940,833

OSCILLATION GENERATOR Filed April 8, 1931 Fr Quen C A. C

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a V/EforJ/V/VdreW #4 W I A r Patented Dec. 26, 1933 UNITED STATESPATE-N'rjo FFIcE A i"1,94o,sss w OSCILLATION GENE ATOR Victor J. A dreWooster, 10hio,' assign'or m WestinghouseElc'ctric & ManufacturingCompany, a corporation of Pennsylvania t I Application April 8, 1931.Serial No. 528,555 21Clain s. (01. 250-36).

My invention relates to an oscillation generator and more particularlyto novel improvements therein for the'accomplishment of certaindesirable results.

'It is a well known phenomenon that; in oscillation generator circuitsembodyingthermionicdevices, the frequency ofthe generated oscillation isa function of the grid-to-filament andv of the plate-to-filamentresistances. Furthermore, the grid-to-filament and the plate-to-filamentresistances severally are functions of the amplitude of oscillations inthe grid and plate circuits.

A regeneration control, constructed according to teachings of the priorart will, therefore, produce changes in the frequency of the generatorwhen the amplitude of oscillations is altered. A regeneration control,comprising a means for varying the potential on the plate of anoscillator, is widely used because the effect of this control onfrequency is small. While the effect on the frequency might be too smallto be considered as a serious disadvantage in most radio circuits, theproblem of reducing oreliminating the effect becomes one of paramountimportance when such oscillators are to be calibrated and employed infrequency-measuring systems for measuring either audio or radiofrequencies.

One object of my invention is to provide a method of controllingregeneration in an oscillator without producing a resultant frequencychange.

Another object of .my invention is to provide, I

dotted line O- 0 of Fig. 2 which indicates he an oscillation generatorcapable of maintaining a substantially constant-frequency output.

Another object of my invention is to provide an oscillation generatorwherein the above objects are accomplished in a very simple andeffective manner. Y Additional objects will be disclosed in thefollowing description of my invention.

y In the accompanying drawing; Figure 1 is a diagram of apparatus andcircuits and Fig. 2 a

curve diagram illustrating the theory of operation of my invention, asapplied to an oscillator of the Colpitt type, together with circuitcharacteristic curves, although it should be understood that myinvention is not necessarily limited,

in its operation, to the above mentioned circuit, but may beincorporated in an oscillation generator of practically any type withequally good results.

An oscillator of the type mentioned comprises a thermionic device 1having an anode 3, cathode 5 and grid '7 and an oscillatory circuitassociated l therewith comprising a pair of serially-connected variablecapacitors 9 "and 11 shunted by an inductor 13. As ,illustratedin thefigure of the drawing, the filament is tied into the. oscillatorycircuit at a point 15 intermediate the capacitors 9 and 11, the anodebeing connected in at one extremity 17 of the inductor and the gridbeing connected to the. other extremitylQ through a grid condenser 21.The customary grid-leak resistor 23 is provided as shown.

. Utilizing a circuit comprising only the elements outlined above, ifasource of potential applied. to the anode of the thermionic device werevaried as a means of controlling regeneration, the frequency of theoscillator would be found to change somewhat as indicated by the curveM-M of Fig. 2. The total change indicated represents but a very smallincrease in frequency which while ordinarily not troublesome would beundesirable for frequency measuring work.

The curve NN of Fig. 2 represents the effect on the frequency of theoscillator produced by variations in a resistor or other impedance whichchange in frequency for changes in regeneration. I have found itpossible to approach this ideal condition very closely, as illustratedby curve I Q-'-Q of Fig. 2, by superimposing, in the same circuit, thereverse effects noted above, the tendency of the frequency to increasedue to-one effect being substantially neutralized by the tendency of thefrequency to decrease because of the other effect. This methodconstitutes animportant feature of my invention. 1

The above result is accomplished, in a very simple manner, by modifyingthe oscillator described above; Referring back to Fig. 1, I provide asource of plate potential 25 connected in series with a plurality ofresistors 27, 29, 31 between the filament and the grid end 19 of theoscillating circuit, the source 25 and resistance 27 being by-passed bya capacitor 33 of low impedance at the oscillation frequency, anapproximate value of the capacity being .01 mfd. A control element,comprising a variable resistor 35, is connected in parallel with thesource of potential and one or both of the resistances 2'7 and 29, forexample, to provide regeneration control through variation of platepotential on the anode of the thermionic device.

' In the position described, the variable resistor, in combination withresistor 31, also constitutes an impedance connected in shuntrelationshipto the condenser 9 whichcomprises a portion of theoscillating circuit, thereby fulfilling the conditions for producing adecreasingfrequency tendency.

Therefore, by the simple operation of altering the value of the resistor35, I am enabled to control regeneration in the circuit and, at the sametime, substantially neutralize the rising frequency characteristic ofthe circuit to obtain a substantially constant frequency output,regardless of the plate-potential variations.

The degree of constancy will depend somewhat upon the values of theresistors 27, 29, 31 in the circuit. Excellent results have beenobtained in the following cases Wherethe values of resistors 29 and 31bearing the ratio of approximately 1.4

to l were employed: I

-- Resistors #27 r #29 #31 #35 ResistoritZ'l may be dispensed withtas itdoes not enter into the fundamental operation of the system. Itsfunction, primarily, is that of a battery filter resistor and,accordingly, is not an essential element, although its function isuseful.

A glance at the curves of Fig. 2 will serve to indicate the constancy offrequency obtained in an oscillation generator, as'a result ofmyinvention.

While I have disclosed my invention in great detail, I do not desire tobe limited thereby except insofar as is necessitated by the prior artand by the appended claims.

I claim as my invention:

1. In combination, an oscillation generator comprising a potentialsupply source and an oscillatory circuit, said supply source beingconnected across a portion of said oscillatory circuit and an impedancein shunt to both said supply source and said portion of said oscillatorycircuit whereby undesired changes in frequency of said generator arisingout of changes in applied potential willbe substantially balanced out.

.2. In combination, an oscillation generator comprisinga source ofpotential and; an oscillatory circuit including a condenser and a coil,said source of-potential being, connected across said condenser, and avariableresistor in shunt to said" source of potential and saidcondenser whereby changes in frequency of said generator due tochangesin potential from said supply source will be substantiallybalanced out.

VICTOR '3. ANDREW.

